It’s been almost two years since the start of the coronavirus pandemic and the U.S. is opening back up. Concerts, sporting events and other activities are making a comeback, but is it safe to attend? While many people have returned to what life was before COVID-19, there’s still precautions doctors suggest the public take in order to help prevent the spread of the virus. Eat This, Not That! Health talked with Dr. J. Wes Ulm, MD, Ph.D., is a physician-researcher and part of the Heroes of the COVID Crisis series who explained the places he’s still cautious to go and why. “This is the dreaded topic we all hoped would be in the rearview mirror by now as the onset of winter 2021 approaches, a full two years into the COVID-19 pandemic,” he says. “Last year at this time, the air was filled with heady predictions of herd immunity just around the corner, as powerful vaccines (with 95 percent efficacy) combined with improved treatments like dexamethasone and remdesivir plus better masking, tracing, and detection tools promised to put the pandemic behind us. Fast-forward a year, and the optimism is much more guarded and cautious, as another year of false dawns gives way to grizzled girding for yet another winter battle in the medical trenches against a relentless foe. What happened? In short, the Delta variant did. The COVID vaccines, as promising as they were and still are, were found to wane significantly in their immune protection after several months and to be leaky, i.e. to provide only limited mucosal immunity at the outset. This allows the virulent Delta variety (and its many mutated sub-variants) to spread even in fully vaccinated communities.”

That’s why you need to be extra careful. Read on for places you shouldn’t go even if they’re open—and to ensure your health and the health of others, don’t miss these Sure Signs You’ve Already Had COVID.

“So which sorts of activities and places should prompt us to exercise a high level of precaution as the 2021 holiday season nears?” he asks. “At the top of the list as far as potential superspreader events, now as during the previous year, are large indoor gatherings with poor ventilation, particularly if voices are raised (and droplets propelled) without masks. Unfortunately—and I say this as a concert and festival-loving musician myself—this includes assemblages like indoor concerts and choir performances, especially if held inside close quarters. Being fully vaccinated and wearing a mask oneself do provide a valuable layer of protection, but again it’s worth reiterating that for the aggressive delta variant, even vaccinated individuals can carry and transmit high titers (measurable quantities) of viral particles of SARS-CoV-2, the virus that causes COVID-19. For delta in particular, recent immunization confers strong but nonetheless somewhat patchy protection, and that immunity shield begins noticeably subsiding by around 3 months and especially at the six-month mark. So particularly if you’re a few months out from your shots or unvaccinated, have one or more serious comorbidities for a COVID-19 bout (notably high blood pressure, obesity, or chronic respiratory disease), or in areas with poor ventilation, take precautions and, as much as possible in that kind of atmosphere, social-distance and wear a good mask, even if stopping short of an N-95 respirator. A COVID-19 encounter is a microbiological roll of the dice, and even if a mask doesn’t fully obviate an infection, preliminary research is indicating that it may help to reduce the SARS-CoV-2 viral load enough to yield a mild case and cut the risk of long COVID syndrome, perhaps thereby even boosting natural immunity through a phenomenon akin to variolation. (See the October 2020 article by Gandhi and Rutherford in the New England Journal of Medicine for a more thorough explanation of this.) Wherever possible, be wary of large packed indoor gatherings (esp. with hundreds or thousands of people), try to encourage that such events be held outdoors — safe patio heaters are becoming ubiquitous — and that ventilation is above pre-pandemic standards if they must be done inside, to optimize airflow and minimize the potential for droplets to convey the virus from person-to-person.”

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Dr. Ulm says, “The holidays are coming up, and we can’t avoid those Thanksgiving table conversations and hugs forever, especially if COVID-19 is indeed becoming endemic. But COVID-19 is spread through both droplets and broad airborne dissemination, so family gatherings are unfortunately one of the prime opportunities for SARS-CoV-2 to leap from person to person, and explain much of the sharply spiking incidence and hospitalizations noted around major community get-togethers. If the prospect of a virtual gathering around the feast table holds little appeal, then once again bear this basic tenet in mind: A COVID-19 bout is a stochastic (random) event after viral exposure, and it’s best to mitigate the risk of a high viral load and exposure potential, even if not possible to eliminate it entirely. Encourage participants in close contact to get tested prior to the trip if they can, and to get a booster if they’re more than six months out — although vaccination (as noted) doesn’t stop transmission of the delta variant, there are studies that indicate some reduction in viral load at mucous membranes, alongside the decrease in risk of hospitalization if one does come down with COVID. Make sure to ventilate interior areas as much as feasible, and when possible, try to hold events outdoors, at least as much as weather permits. Likewise, even though the masks come off for dining and extended conversations, it helps to have them on whenever possible outside of such occasions. Remember, even if you have a rendezvous with SARS-CoV-2 over the holidays, best to make sure it’s as gentle and minimal as possible!”

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Dr. Ulm reveals why he’s still wary of taking public transportation, especially during the holidays. “Bus, train, and airline operators have done a solid job of ventilating their compartments well, greatly reducing the risk of COVID exposure. Nevertheless, large gatherings of strangers in cramped quarters represent the ideal breeding ground for COVID-19 spread, and for delta this includes vaccinated individuals. Transportation firms vary in their adherence to mask guidelines, but the holiday season isn’t the time when you want to be stuck in a small area with maskless individuals spreading droplets to-and-from — particularly when concurrent cold and flu seasons are raising the incidence of coughing spells as a whole! Transportation operators and inspectors generally provide readily available data on mask usage and adherence, and this is one of those times when you’ll want to guide your selection based on how well passengers mask up. It’s never pleasant to be a couple seats down from someone hacking and coughing, but amid the pandemic, this takes on a much more immediate significance.”

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“Business, research, and product conferences tend to have less droplet transmission of COVID-19 by virtue of their very subject matter; loud singing, whooping, and cheering have a way of spreading virus-containing droplets as much as sneezes and productive coughs, so the comparatively drier (usually) verbal subject matter of major symposia or exhibitions tends to reduce these hazards,” Dr. Ulm says. “But as with any indoor event, airborne transmission is a constant peril especially if ventilation is inadequate, and a single contagious individual can become a mass superspreader particularly for the highly virulent delta variant. It’s for this reason that even now, most such conferences are being held online, but if you must attend in-person, try to choose those conferences which entail COVID testing shortly before attendance. Once again, keep in mind that the delta variant replicates so efficiently that even fully vaccinated individuals can still spread it, so pre-conference testing provides an extra buffer of protection to minimize a potential superspreader fiasco.”

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Dr. Ulm explains, “If there’s a tiny saving grace about COVID-19, it’s that the virus behind it at least is relatively inefficient at spreading outdoors. This is because the viral particles, when transmitting as aerosols, tend to dissipate rapidly in the surrounding air, which means that picnics, parks, and athletic powwows in large stadiums are, thankfully, comparatively safe. Still, it’s again worth noting that COVID-19 also spreads through droplets particularly in close quarters, which can be a factor even for outdoor events — and those droplets may contain a worrisomely high viral load if inhaled by a bystander or transmitted by a touch to the eyes or mucous membranes, especially amid the passionate cheers and jeers of major sports events. Try to find seating that’s distanced from the loud applause in the bleachers behind you, and wash your hands or use hand sanitizer wherever possible particularly if a cheer has spread throughout the aisles. And for this scenario plus all four of the ones above, if you do start manifesting symptoms, the CDC recommends testing within 5-7 days of the event or likely exposure. Even if the winter of 2021-2022 is shaping up to be another grueling battle with our persistent microbial foe, we now have far more tools for treatment and interventions at our disposal than in the previous winter, and so you’ll want to be diagnosed and treated as soon as possible.”

Follow the public health fundamentals and help end this pandemic, no matter where you live—get vaccinated ASAP; if you live in an area with low vaccination rates, wear an N95 face mask, don’t travel, social distance, avoid large crowds, don’t go indoors with people you’re not sheltering with (especially in bars), practice good hand hygiene, and to protect your life and the lives of others, don’t visit any of these 35 Places You’re Most Likely to Catch COVID.

Dr. J. Wes Ulm, MD, Ph.D., is a physician-researcher, musician (J. Wes Ulm and Kant’s Konundrum), and novelist, and earned a dual MD/Ph.D. degree from Harvard Medical School and MIT. He is part of the Heroes of the COVID Crisis series in relation to his ongoing efforts in the drug discovery and public health arena.